1. Technical Field
The invention relates to a jacket for flexible heat-insulated conduits.
2. Description of the Background Art
EP 0 897 788 discloses a heat-insulated conduit that is made up of an internal tube, a heat-insulating layer based on polyurethane foam and surrounding the internal tube, and an external jacket. The known conduit can be manufactured in long lengths in one continuous working step. The external jacket, manufactured by extrusion, is made of polyethylene and has a corrugated surface.
One important field of application for the known conduit is the transport of district heat, in which context the conduit is installed in the ground.
The jacket of the conduit is exposed to considerable mechanical loads during both manufacture and installation. By being wound onto cable drums, the jacket is stressed by tensile and flexural forces. Upon installation in the ground, the jacket is stressed by frictional forces. These forces are handled by a conventional jacket made of polyethylene.
On the other hand, the good mechanical strength values of the jacket also result in greater stiffness of the conduit, so that the bending radius cannot fall below a certain value. The known conduit is transported to the utilization site either on commercially available cable drums or coiled into a ring. Large diameters for the cable drums on which the conduit is wound, or large-diameter rings, create problems upon transport to the installation site. A conduit having little flexibility proves disadvantageous during installation as well, since the conduit cannot be curved around tight radii.